1. Field of the Invention
The present invention concerns a method and device for processing waste issuing from the nuclear industry. It relates more particularly to a method and device for limiting the degassing of tritiated waste produced by nuclear reactions.
2. Description of the Related Art
Tritium (T or 3H) may be present in several types of nuclear reactor. In the majority of fission reactors, it may for example be produced by the ternary fission of uranium (U) and plutonium (Pu) as well as in neutron reactions between boron (B) and lithium (Li). In addition, in fusion reactors, tritium is used as a fuel. That is the case of Joint European Torus (JET) reactors, for International Thermonuclear Experimental Reactors (ITER) and (Demonstration Power Plant (DEMO reactors) designed to succeed the ITER reactor. In these reactors, the fusion reaction from deuterium (D or 2H) and tritium (T or 3H) is governed by Equation (1):D+T→42He+01n+17.6 MeV  (1)
One of the properties of tritium, just like the other isotopes of hydrogen, is its ability to penetrate through materials, which contaminates them. This property makes tritiated waste very specific since both the radioactive elements and the degassing must be taken into account in the management of the waste. Moreover, tritium may be present in two gaseous forms, tritiated hydrogen (HT or T2) and tritiated water (HTO or T2O). It should be noted that tritiated hydrogen (HT or T2) is much more mobile than tritiated water (HTO or T2O), even in vapour form. Tritiated hydrogen (HT or T2) also has a very small size. Its great mobility and its small size promote its diffusion even through the finest porosities, passing for example through rubber and diffusing in the majority of types of steel and concrete. Trapping tritiated hydrogen (HT or T2) is therefore made particularly complex.
With the development of fusion reactors, the quantity of tritiated waste will thus increase significantly. There consequently exists a particularly great need consisting of sizing an effective method of detritiation and limitation of degassing, in particular at ambient temperature and atmospheric pressure. The reduction in the quantity of tritiated hydrogen produced by a package of waste must be sufficiently effective to satisfy the existing acceptability criteria of warehousing and storage centres, so that these packages comprising tritiated waste can be included in the existing warehousing and storage centres.
One solution has been proposed and is described in U.S. Pat. No. 5,464,988. This patent proposes a device for storing and transporting tritiated water contained in a gas. The device comprises an external drum and an internal drum placed inside the external drum. Inside the internal drum is a disposable molecular sieve intended to be loaded with tritium. The device also comprises entry and exit diffusers as well as a catalytic hydrogen recombiner. A protective and thermal insulation material is arranged in each space available between the two drums. The catalytic hydrogen recombiner converts the tritiated hydrogen into tritiated water, which can then be trapped by the molecular sieve in solid form with a view to storage and transportation thereof.
This device affords a solution for trapping tritiated water in gaseous form. Trapping tritiated hydrogen (HT or T2) does however prove to be more complicated because of the smaller size and greater mobility of this gas compared with tritiated water in gaseous form. In addition, this solution is based on a particularly complex drum requiring numerous specific items of equipment that require specific maintenance. For example, the use of a catalytic recombiner requires a heating device and therefore maintenance of the system. In addition, human intervention is necessary for regularly changing the molecular sieve saturated with tritiated water.
The complexity of this solution tends to make its cost relatively high and its reliability limited.
There therefore exists a need consisting of proposing a simple and effective solution for limitation of the degassing of tritiated hydrogen (T2 or HT) and tritiated water (HTO or T2O), this solution also having to make it possible to reduce the maintenance and human intervention requirements. The solution must also be effective over several hundreds of years.
The objective of the present invention is to describe such a solution.